It is known to provide rigid polyisocyanurate (PIR) foams for uses such as building insulation. Such foams are conventionally manufactured by the provision of a polyol component and an isocyanate component, one or both of these components optionally containing other ingredients such as surfactants, catalysts, etc., blending a blowing agent, often pentane, with the polyol component or the isocyanate component (usually the polyol component) and mixing the two in order to induce foaming.
It would be desirable to be able to improve the production efficiency of such methods, especially to improve the efficiency and effectiveness of the step of mixing the pentane blowing agent with the polyol component.
Such pentane-blown PIR foams are commonly characterised by their lambda value, which is a measure of their thermal conductivity. A lower value of lambda is beneficial as it signifies lower thermal conductivity and consequently good insulation properties. Pentane-blown PIR foams can exhibit good insulation properties when first formed but there is a tendency for their insulation properties to deteriorate over time, either on storage or when in position for use. Namely, the value of lambda tends to increase. It would be desirable to be able to provide pentane-blown PIR foams which exhibit reduced deterioration in lambda value over time.
WO 2010/054317 describes a pentane-blown PIR foam. However, the method disclosed will suffer from the problem that polyols are difficult to mix with pentane owing to pentane's poor miscibility with polyols. This problem can be overcome by the addition of man-made vitreous fibres, according to the first aspect of the invention as described below.